A bag contains n balls numbered 1, 2, 3, ....n. Two of them are taken out of the bag (without replacement). Let X be the maximum value among the two selected balls.
(a) Find the mean E(X) when n=5.
(b) Generalize to any n.

There are only ways to choose 2 items from 5.
You can easily list them out .
From which you can see and .